1. Field of the Invention
This invention relates generally to a method and apparatus for the high temperature decomposition of hydrogen peroxide to form oxidative free radicals, such as, hydroxyl radical (HO) and hydroperoxyl radical (HOO.), which oxidize nitric oxide (NO) to nitrogen dioxide (NO2).
2. Description of the Background Art
Power plants produce a large amount of nitric oxide that must be removed from exhaust gas streams before the gas stream may be emitted into the environment. Effective removal of nitric oxide from the gas stream is complicated by its low water solubility. Although water scrubber systems may be used to aid in the removal of nitric oxide from the gas streams, the effectiveness of the water scrubber system may be increased by oxidizing the nitric oxide to nitrogen dioxide. Nitrogen dioxide is more water soluble than nitric oxide and can be easily removed from the gas streams using various removal processes, such as the water-based scrubber systems. Although nitric oxide does slowly oxidize in air to nitrogen dioxide, an effective oxidizing agent is needed to make the oxidation of nitric oxide effective at low concentrations (˜25 to 350 ppm). This low concentration of NO represents a target planned by the US EPA for power plant applications. By 2004, the EPA will require that coal and oil fired power plants install new controls that lower the NOx emissions to 110 ppm. The 2004 requirement for natural gas NOx emissions will be lowered in 2004 to 50 ppm. Currently, the Selective Catalytic Reduction (SCR) method is the only technology that can meet these 2004 EPA requirements.
Gas-phase oxidation of nitric oxide to nitrogen dioxide may be increased by using ozone, hydrogen peroxide, atomic oxygen, hydroxyl radicals or hydroperoxyl radicals as oxidizing agents. The problems with these materials are their high cost and complexity. Injection of hydrogen peroxide in a heated (300 to 400° C.) nitric oxide gas stream or the introduction of an ultraviolet light source to decompose hydrogen peroxide to form oxidative free radicals are examples of known technology with high processing costs. Another expensive material that has been used to oxidize nitric oxide is ozone. A need therefore exists for a highly effective and low cost method for oxidation of nitric oxide.